1. Field of the Invention
The present invention relates to an automatic frequency control device in an OFDM (Orthogonal Frequency Divisional Multiplexing) transmission system and a method thereof.
2. Description of the Related Art
Recent advancements in communication technologies have been remarkable and systems communicating large amounts of data at high speed have been being realized. The phenomenon not only applies to wired communication, but also wireless communication. Specifically, with the spread of mobile terminals, such as cellular phones and the like, research and development has created wireless systems where a large amount of data can be communicated at high speed, and multimedia data, such as dynamic images, voice and the like, can be handled by mobile terminals.
Recently, high-speed wireless communication based on CDMA called “the third generation” has been developed and is about to be put into practical use. In response to this trend, wireless communication R&D departments have started to research and develop the fourth generation wireless communication system aiming at larger-capacity and higher-speed wireless communication.
OFDM-CDMA is a strong candidate for the basic system of the fourth generation mobile communication system. In this system, an OFDM technology for transmitting a plurality of pieces of information in parallel using a plurality of sub-carriers each with a reciprocally orthogonal frequency and a CDMA technology using the orthogonality of a spread code by which user data is multiplied when a plurality of pieces of user data are multiplexed, are united in order to realize larger-capacity, higher-quality and higher-speed communication.
However, currently the OFDM-CDMA system is still in a proposal stage and in an R&D evaluation stage, and individual technologies required for an actual system must still be developed.
In particular, in a system based on multi-carrier transmission, such as an OFDM-CDMA system and the like, it is important to reproduce a prescribed carrier frequency in a receiver. In particular, the control accuracy of a reproduced carrier frequency is very important.